Re: [PATCHv2] x86/xen: during early setup, only 1:1 map the ISA region

[Aurelien Chartier <aurelien.chartier@citrix.com>]

On 25/07/13 18:33, Konrad Rzeszutek Wilk wrote:
> David Vrabel <david.vrabel@citrix.com> wrote:
>> On 25/07/13 16:46, Aurelien Chartier wrote:
>>> On 22/07/13 15:29, David Vrabel wrote:
>>>> From: David Vrabel <david.vrabel@citrix.com>
>>>>
>>>> During early setup, when the reserved regions and MMIO holes are
>> being
>>>> setup as 1:1 in the p2m, clear any mappings instead of making them
>> 1:1
>>>> (execept for the ISA region which is expected to be mapped).
>>>>
>>>> This fixes a regression introduced in 3.5 by 83d51ab473dd
>> (xen/setup:
>>>> update VA mapping when releasing memory during setup) which caused
>>>> hosts with tboot to fail to boot.
>>>>
>>>> tboot marks a region in the e820 map as unusable and the dom0 kernel
>>>> would attempt to map this region and Xen does not permit unusable
>>>> regions to be mapped by guests.
>>>>
>>>> (XEN)  0000000000000000 - 0000000000060000 (usable)
>>>> (XEN)  0000000000060000 - 0000000000068000 (reserved)
>>>> (XEN)  0000000000068000 - 000000000009e000 (usable)
>>>> (XEN)  0000000000100000 - 0000000000800000 (usable)
>>>> (XEN)  0000000000800000 - 0000000000972000 (unusable)
>>>>
>>>> tboot marked this region as unusable.
>>>>
>>>> (XEN)  0000000000972000 - 00000000cf200000 (usable)
>>>> (XEN)  00000000cf200000 - 00000000cf38f000 (reserved)
>>>> (XEN)  00000000cf38f000 - 00000000cf3ce000 (ACPI data)
>>>> (XEN)  00000000cf3ce000 - 00000000d0000000 (reserved)
>>>> (XEN)  00000000e0000000 - 00000000f0000000 (reserved)
>>>> (XEN)  00000000fe000000 - 0000000100000000 (reserved)
>>>> (XEN)  0000000100000000 - 0000000630000000 (usable)
>>>>
>>>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>>>> ---
>>>> v2: Extend 1:1 mapping region to cover 0 - 1MiB. find_ibft_region()
>>>> scans from 512 KiB and if this overlapped with a reserved region it
>>>> would crash.
>>> I made more extensive testing and I was wrong, the crash I reported
>> has
>>> been fixed upstream. I am able to boot a 3.11-rc1 kernel without any
>>> patch applied. However, I am still seeing errors in the log :
>>>
>>> (XEN) mm.c:901:d0 Error getting mfn 800 (pfn 5555555555555555) from
>> L1
>>> entry 0000000000800463 for l1e_owner=0, pg_owner=0
>>>
>>> David's patch is fixing those errors.
>>>
>>> I also tried applying that patch to 3.8.13.4, but dom0 was still
>>> crashing at boot time :
>> Does this
>> (http://lists.xen.org/archives/html/xen-devel/2013-07/msg00701.html)
>> patch work better?

This patch was fixing the crash on 3.8.13.x, but I did not test it with
3.11.

I will try to find which commit fixed the crash I reported between those
two versions.


>>
>> I do think hiding UNUSABLE regions from dom0 is the right thing to do
>> and will be a more reliable fix going forwards, but Konrad didn't
>> agree.
>>
>> David
> It well might but we need to:
>  -  Know why it is still happening after a fix that is tailored towards the fix and still does not work with stable kernels.  What are we missing? 
>  -  it is unclear to me how this will affect PV DomU with PCI pass through which use  e820_hole parameter -  which means that the e820 in the guest is similar to the host one. We can't break them.